The present invention relates to an eccentric plate grinding machine with a braking means for limiting the rotary speed of the grinding plate.
The European patent document EP 0 559 020 B1 discloses such an eccentric plate grinding machine in which the grinding plate can be braked by a ring-shaped braking means arranged in the housing. The braking force can be reproducibly exactly adjustable.
In order to maintain the dimensions of the grinding machine as compact as possible and to provide a good handling, a small structural height of the friction ring is required. The friction ring must be especially small, and it is difficult to produce since all tolerances occurring during the series production of the contributing components such as the housing, the bearing or the bearing receptacle must be compensated to guarantee a constant braking action. Simultaneously the braking force under working conditions must not be too high to avoid an increased wear of the components. The filigrane and highly accurate design of the braking means leads to an expensive and complicated manufacture.
Accordingly, it is an object of the present invention to provide an eccentric plate grinder which avoids the disadvantages of the prior art.
More particularly, it is an object of present invention to provide an eccentric plate grinder, in which the braking force is automatically limited by valve-shaped flaps in the friction ring.
It is especially advantageous when power-reinforcing vacuum cleaner is connected to the eccentric plate grinding machine, since with its use a high alternating negative pressure is produced in the region of the commercial conventional friction ring. Thereby it is strongly pressed against the grinding plate, and heat is generated by high friction force. Since both braking means and the grinding plate are composed of synthetic plastic, for example rubber they are loaded with charge and wear prematurely. With the valve-shaped flaps the advantages of high suction power can be obtained without influencing the service life of the braking ring.
It is especially advantageous when the friction ring at its side which faces away from the section chamber is provided with a circumferential ring groove, which reduces the wall thickness and is provided with an elastic lip which adjoins it and extends in an axial direction toward the grinding plate. With the circumferential ring groove, the force characteristic line of the spring characteristic of the friction ring is maintained very flat. This means that the friction force, with which the braking means press against the grinding plate is approximately independent from the distance between the housing and the grinding plate by which the tolerances are determined.
It is further advantages when the region of the ring groove is formed as an elastic hinge for the movability of the elastic lip relative to the friction ring. With this film-hinge-shape connection, the movability of the elastic lip relative to the friction ring is reinforced.
It is especially advantageous when the friction ring has a U-shaped cross-section, such that its U-leg regions engage the side, preferably the end side, of the lower region and held on them. Thereby a simple, fast and light mounting of the friction ring on the housing is possible.
Moreover, it is advantageous when a further leg is connected with an inner U-leg region. It has a reduced cross-section and extends inclinedly inwardly and downwardly. It is angled inclinedly outwardly in the region of the ring groove and forms there a lip.
A further leg in this manner, because of its inclined course, is sufficiently great to carry the valve-shaped flaps. Furthermore the V-shape which is formed of the further leg and the lip contributes to a flat characteristic line for the pressing force of the lip on the upper side of the grinding plate.
Moreover, it is especially advantageous when the ring-shaped braking means have a greater diameter than the lower region of the cylindrical housing, so that the braking means extend beyond the outer contour of the housing as a bumper. The braking means prevent therefore efficiently the abutment of harder housing regions against the workpiece so as to avoid damages of the workpiece.
When the valve-shaped flaps of the friction ring moreover are formed as U-shaped or partial circle-shaped punched out sections it provides for fast, inexpensive and efficient manufacture.
Moreover, it is advantageous when the film-hinge-shaped mounting regions of the flap are formed as punched-in sections.
The gaps of the punched-in sections regulates the suction force with which the flaps are to be open, and also regulate the braking force which acts on the grinding plate.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.